1. Field of the Invention
The present invention relates to a process for etching silicon-based materials mainly of a character having disposed on a substrate either one or both of a silicon layer and a silicon-containing layer. Such process is suitable particularly for use in etching so-called polycide structures in the manufacture of semiconductors.
2. Description of the Related Art
As is generally know in the art of electronic components such as semiconductors and the like, those materials comprised of a substrate and at least one silicon layer laminated thereon can be etched for patterning. One typical material has superposed on a substrate a silicon layer and a high-melting silicide layer, finding its use for gate wirings on semiconductors.
High-melting silicides are advantageous as they are smaller in sheet resistance than polycrystalline silicons commonly acceptable as gate wiring materials for conventional circuits of a large-scale integration type (LSI). Further, the silicide when superposed on a silicon layer or a polysilicon layer in particular has been formed to retain the resultant interface at a highly reliable level. This reliability is seen at an interface defined by such a silicon layer together with silicon dioxide (SiO.sub.2) as a gate-insulating film.
The above silicon-silicide composite material is usually named a polycide structure from lamination of a silicide on a polysilicon.
As a result of the advent of high-speed LSI circuits, polycide structures have recently become prominent for gate formation. This entails various modes of etching.
To attain desired patterning, a given polycide structure is required to be etched with its two different layers held in anisotropic relation to each other. A family of gases know as chlorofluorocarbons (CFC) has been used among which is typified 1,1,2-trichloro-1,2,2-trifluoroethane (C.sub.2 Cl.sub.3 F.sub.3) (CFC113). These gases, however, are reported to rise into the stratosphere and to erode the ozone layer, posing serious environmental problems. Warnings are being made to phase out the use of such ozone-depleting chemicals.
Great concern has been directed toward the prevision of a substitute gas which is highly capable of exerting an anisotropic action on both silicon and high-melting silicide layers, thus ensuring etching in good shape. Hydrogen bromide (HBr) attracts much attention, for its inherent ability to etch with high anisotropy and high selectivity, as a replacement for the CFC gases. One problem with HBr is that no method is established for detecting the end point of etching in the case where the gas is used alone. This means that HBr does not warrant commercial acceptance in etching silicon-based materials for gate formation.
The present inventors have previously found that polycide structures can be etched into the form of films at increased rates of production and with improved magnitudes of anisotropy and selectivity as disclosed in Japanese Patent Application No. 2-10489. This mode of etching is designated to use a mixture of an HBr gas with a fluorine radical-donating gas such as sulfur hexafluoride (SF.sub.6). The HBr-SF.sub.6 gas is undesirable for etching a silicon layer such as of a doped polysilicon (DOPOS) under the same etch conditions as in a high-melting silicide layer such as of a tungsten silicide (WSi.sub.x). The silicon layer is necessarily susceptible to objectionable side etching.